API docs (#379)

* Move API documentation into separate directory

* Rearrange main docs bar

* Split python examples into separate page

* Fix broken links

* Adds page for browseable API

* Fix image links

* Add entrypoint page for barcodes

* Update barcode docs

* Add (empty) pages for internal and external barcods

* Add documentation on "internal" barcode format

* Documentation for external barcode functionality

* Skeleton page for custom barcode information

* Extend docs for custom barcodesplugins

* Add stubs for new API docs

* Add documentation for downloading data via the AP

* API metadata information

* docs for pythonic metadata access

* docs for bulk delete

docs/barcodes/internal.md

@@ -0,0 +1,36 @@
+---
+title: Internal Barcodes
+---
+
+## Internal Barcodes
+
+InvenTree defines an internal format for generating barcodes for various items. This format uses a simple JSON-style string to uniquely identify an item in the database.
+
+Some simple examples of this format are shown below:
+
+| Model Type | Example Barcode |
+| --- | --- |
+| Part | `{% raw %}{"part": 10}{% endraw %}` |
+| Stock Item | `{% raw %}{"stockitem": 123}{% endraw %}` |
+| Supplier Part | `{% raw %}{"supplierpart": 99}{% endraw %}` |
+
+The numerical ID value used is the *Primary Key* (PK) of the particular object in the database.
+
+## Report Integration
+
+This barcode format can be used to generate 1D or 2D barcodes (e.g. for [labels and reports](../report/barcodes.md))
+
+To access the raw barcode information string within a template, use the `.barcode` attribute, and pass it into a barcode generation method.
+
+### Example: QR Code
+
+For example, to render a QR-Code image for a part instance:
+
+```html
+{% raw %}
+<img src='{% qrcode part.barcode %}'>
+{% endraw %}
+```
+
+!!! info "Barcode Formatting"
+    Refer to the [report documentation](../report/barcodes.md) for further information on formatting barcode data